With respect to photographic images composed of silver, the ratio of optical density of the images to silver content in a unit area of the images is generally called the covering power. The covering power is a measure for evaluating optical efficiency of silver composing the images. The covering power of the silver halide photographic light-sensitive layer generally increases with a decrease of the particle size of silver halide particles and reduces with an increase of the particle size thereof. On the other hand, the sensitivity of the silver halide emulsion layer generally becomes high with an increase of the particle size of silver halide particles. Thus, silver halide emulsions having a larger particle size are used to produce photographic light-sensitive materials having high sensitivity. Accordingly, the photographic light-sensitive materials having high sensitivity require a large silver content per unit area for obtaining a definit image density. Namely, in order to obtain both high sensitivity and the required maximum image density, it is necessary that the photographic light-sensitive material contains a larger amount of silver salts per unit area. This is an undesirable feature of the conventional photographic light-sensitive materials having high sensitivity.
The particle size of silver halide in the present invention means the diameter of particles when the particles are spherical or nearly spherical, or means the diameter of a sphere having the same volume when the particles have other shapes (for example, cube or plate, etc.).
Attempts at improving the covering power while maintaining high sensitivity which comprise adding various kinds of polymer to silver halide emulsions having highly sensitive coarse particles have been described in British Patent Nos. 1,048,057 and 1,039,471 and U.S. Pat. Nos. 3,043,697 and 3,446,618. However, these techniques are not suitable because the effect for improving the covering power is insufficient and strength of the coating film is reduced. Particularly, when a light-sensitive material having a coating film of poor strength is used in an automatic developing apparatus which are now conventionally used, some of the gelatin in the film dissolves in the developing solution or the fixing solution, adheres to conveying rolls of the automatic developing apparatus, and transfers to the light-sensitive material. This causes pollution of the photographic images.
On the other hand, it has been described in U.S. Pat. Nos. 2,996,382 and 3,178,282 that photographic images having high contrast and high covering power are obtained in a high sensitivity by using silver halide photographic light-sensitive materials wherein coarse particles of surface latent image type silver halide and fine silver halide particles having fog nuclei in the inner part thereof are contained in the same layer or adjacent layers. According to this process, it is supposed that coarse particles of surface latent image type silver halide are first developed and products resulting from the development attack neighboring fine silver halide particles having fog nuclei in the inner part thereof to cause development of the fine silver halide particles.
However, in this process, since the coarse particles having high sensitivity and the inside fogged fine particles are used, developed silver easily forms a large mottle which causes deterioration of granularity. Further, the color of the resulting images becomes brownish. Moreover, irregular stains are formed on the photographic material when it is allowed to pass directly through the fixing bath from the development bath by means of an automatic developing apparatus without passing through the stopping bath.